Ionic Nitrogen-Doped Carbon Dots as Nonpolar Lubricant Additives at Low Effective Addition

The poor compatibility with nonpolar lubricant still hinders the application of carbon dots (CDs) in lubrication. In addition, research proves that the existence of ionic structure and active groups on CDs are conducive to their lubricity. In order to obtain the ionic structures and good oil compatibility synchronously, a kind of ionic nitrogen-doped CDs (NCDs) was synthesized via the alkylation of nitrogen in NCDs and anion exchange. The new material could exhibit good tribological performance as poly alpha olefins (PAO4) additives with low addition. Moreover, an ionic liquid, [N44HH][DEHP], with the same anion was chosen as a comparison to investigate the role of NCD cations. The surface analyses demonstrate that NCD cations and phosphate ester anions adsorb on the friction interface to play a synergistic lubrication role during the friction process, which could generate a superior carbon-based tribofilm.